From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AH8x227xAinDU3zr33GJYpg5SsDmvTxcWTW5pnqggYfy9nTuWddg14hqBSOgwcDarGKVZewxjJYk ARC-Seal: i=1; a=rsa-sha256; t=1516724598; cv=none; d=google.com; s=arc-20160816; b=SaqsQTJciE/+ShkAdU2Tfj+OGyoYTzhTgLYByLcZBIsUxsv9z9Gtz3yH0kO+dRCNSV nJG9nOo4RtFQvIK+TWqSETITtvkikx88aS9FhQ1fFooQJ0zeXySSvw2aLSopwYR8Rnyx orSSdP8f05HHrOY7Mlqs/68RX4e4FXnkO3IKA7pgTzP5satAFC/JHG2K/gzXAa+oVC+V 62i6Fegj55UVu/T+YOz2C1YQaT70LZkJwYMxBhq9a3g89UEgGgoUpBRRLliBarrnO2RP v1Io+xA1Zuqz8UvVTlM385cCeD2NVIlnJ3/DGU+FtVQpwowHfTA8ZmFwxvJv8B4ChcSf emeg== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=mime-version:accept-language:in-reply-to:references:message-id:date :thread-index:thread-topic:subject:cc:to:from:mime-version :dkim-signature:arc-authentication-results; bh=lVOHswo7KfyDMrb4XSwM1ZuWwPUYyLRlQ1YMpdxUbCk=; b=ORG1VOwRly1OAQ6Wg1PnHs+7kjAvYYIMbzWruxuHf/qvTsoNDJw85rOAD28U8p+1fa pwLxGvVZR+g2nwgWrQJw4wp6dO93yGH2OI1v25fl+ZH3iF56jkoqF3Jum4W6Ji1A0nVY og5BhuMhaEXB3bm46FU5+sQcxNIJWBlwOJf1d02RV8kitKLcNi53z4CLIEBHZnzUJfUX HdQ0WaYzLPNxaJ1PeQyQvl76Am3+J9wg6Gh9mogXXeIwF8NZhAOPy++n1uIC2mSjhBlL TmIqB920f/3Zax1J5Y2G5lhUBnq+nBZY/GIheu1PTlV9FbOpejHSO+Zajcj09c6rI9oK l/0g== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@amazon.co.uk header.s=amazon201209 header.b=fivBvzxo; spf=pass (google.com: domain of prvs=5548949a8=dwmw@amazon.co.uk designates 207.171.190.10 as permitted sender) smtp.mailfrom=prvs=5548949a8=dwmw@amazon.co.uk; dmarc=pass (p=QUARANTINE sp=QUARANTINE dis=NONE) header.from=amazon.co.uk Authentication-Results: mx.google.com; dkim=pass header.i=@amazon.co.uk header.s=amazon201209 header.b=fivBvzxo; spf=pass (google.com: domain of prvs=5548949a8=dwmw@amazon.co.uk designates 207.171.190.10 as permitted sender) smtp.mailfrom=prvs=5548949a8=dwmw@amazon.co.uk; dmarc=pass (p=QUARANTINE sp=QUARANTINE dis=NONE) header.from=amazon.co.uk X-Amazon-filename: smime.p7s X-IronPort-AV: E=Sophos;i="5.46,402,1511827200"; d="p7s'?scan'208";a="716821790" Content-Type: multipart/mixed; boundary="===============8862384844361713452==" MIME-Version: 1.0 From: "Woodhouse, David" To: "thomas.lendacky@amd.com" , "luto@amacapital.net" , "Raslan, KarimAllah" CC: "kvm@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "peterz@infradead.org" , "ashok.raj@intel.com" , "arjan@linux.intel.com" , "arjan.van.de.ven@intel.com" , "bp@suse.de" , "torvalds@linux-foundation.org" , "tglx@linutronix.de" , "Janakarajan.Natarajan@amd.com" , "tim.c.chen@linux.intel.com" , "ak@linux.intel.com" , "joro@8bytes.org" , "dan.j.williams@intel.com" , "x86@kernel.org" , "hpa@zytor.com" , "aarcange@redhat.com" , "mingo@redhat.com" , "luto@kernel.org" , "pbonzini@redhat.com" , "gregkh@linuxfoundation.org" , "dave.hansen@intel.com" , "mhiramat@kernel.org" , "asit.k.mallick@intel.com" , "jun.nakajima@intel.com" , "labbott@redhat.com" , "rkrcmar@redhat.com" Subject: Re: [RFC 09/10] x86/enter: Create macros to restrict/unrestrict Indirect Branch Speculation Thread-Topic: [RFC 09/10] x86/enter: Create macros to restrict/unrestrict Indirect Branch Speculation Thread-Index: AQHTkiQ0iyjGMUW5uUybCpLmt+1puKN+s8qAgALx8gCAAAJHgA== Date: Tue, 23 Jan 2018 16:20:58 +0000 Message-ID: <1516724457.9521.156.camel@amazon.co.uk> References: <1516476182-5153-1-git-send-email-karahmed@amazon.de> <1516476182-5153-10-git-send-email-karahmed@amazon.de> <243BE571-AF73-44B3-8D17-193F9E07686A@amacapital.net> <4e01a7a9-29e4-adcc-3f53-550fb7f3d370@amd.com> In-Reply-To: <4e01a7a9-29e4-adcc-3f53-550fb7f3d370@amd.com> Accept-Language: en-GB, en-US X-MS-Has-Attach: yes X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.43.61.91] MIME-Version: 1.0 X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1590140582166248265?= X-GMAIL-MSGID: =?utf-8?q?1590401012398359883?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: --===============8862384844361713452== Content-Language: en-US Content-Type: multipart/signed; micalg=sha-256; protocol="application/x-pkcs7-signature"; boundary="=-Jf78ZZFQ9Uwj32cTncm4" --=-Jf78ZZFQ9Uwj32cTncm4 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Tue, 2018-01-23 at 10:12 -0600, Tom Lendacky wrote: >=20 > >> +.macro UNRESTRICT_IB_SPEC > >> +=C2=A0=C2=A0=C2=A0 ALTERNATIVE "jmp .Lskip_\@", "", X86_FEATURE_IBRS > >> +=C2=A0=C2=A0=C2=A0 PUSH_MSR_REGS > >> +=C2=A0=C2=A0=C2=A0 WRMSR_ASM $MSR_IA32_SPEC_CTRL, $0, $0 > >=C2=A0 > I think you should be writing 2, not 0, since I'm reasonably > confident that we want STIBP on.=C2=A0 Can you explain why you're writing > 0? >=20 > Do we want to talk about STIBP in general?=C2=A0 Should it be (yet anothe= r) > boot option to enable or disable?=C2=A0 If there is STIBP support without > IBRS support, it could be a set and forget at boot time. We haven't got patches which enable STIBP in general. The kernel itself is safe either way with retpoline, or because IBRS implies STIBP too (that is, there's no difference between writing 1 and 3). So STIBP is purely about protecting userspace processes from one another, and VM guests from one another, when they run on HT siblings. There's an argument that there are so many other information leaks between HT siblings that we might not care. Especially as it's hard to *tell* when you're scheduling, whether you trust all the processes (or guests) on your HT siblings right now... let alone later when scheduling another process if you need to *now* set STIBP on a sibling which is no longer save from this process now running. I'm not sure we want to set STIBP *unconditionally* either because of the performance implications. For IBRS we had an answer and it was just ugly. For STIBP we don't actually have an answer for "how do we use this?". 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Registered in England and Wales with regist= ration number 08650665 and which has its registered office at 60 Holborn Vi= aduct, London EC1A 2FD, United Kingdom. --===============6232099091856861673==-- --===============8862384844361713452==-- From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Woodhouse, David" Subject: Re: [RFC 09/10] x86/enter: Create macros to restrict/unrestrict Indirect Branch Speculation Date: Tue, 23 Jan 2018 16:20:57 +0000 Message-ID: <1516724457.9521.156.camel@amazon.co.uk> References: <1516476182-5153-1-git-send-email-karahmed@amazon.de> <1516476182-5153-10-git-send-email-karahmed@amazon.de> <243BE571-AF73-44B3-8D17-193F9E07686A@amacapital.net> <4e01a7a9-29e4-adcc-3f53-550fb7f3d370@amd.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=sha-256; protocol="application/x-pkcs7-signature"; boundary="=-Jf78ZZFQ9Uwj32cTncm4" Cc: , Andi Kleen , "Andrea Arcangeli" , Andy Lutomirski , "Arjan van de Ven" , Ashok Raj , "Asit Mallick" , Borislav Petkov , "Dan Williams" , Dave Hansen , Greg Kroah-Hartman , "H . Peter Anvin" , Ingo Molnar , Janakarajan Natarajan , Joerg Roedel , "Jun Nakajima" , Laura Abbott , "Linus Torvalds" , Masami Hiramatsu , Paolo Bonzini , Andy Lutomirski , KarimAllah Ahmed Return-path: In-Reply-To: <4e01a7a9-29e4-adcc-3f53-550fb7f3d370@amd.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org --=-Jf78ZZFQ9Uwj32cTncm4 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Tue, 2018-01-23 at 10:12 -0600, Tom Lendacky wrote: >=20 > >> +.macro UNRESTRICT_IB_SPEC > >> +=C2=A0=C2=A0=C2=A0 ALTERNATIVE "jmp .Lskip_\@", "", X86_FEATURE_IBRS > >> +=C2=A0=C2=A0=C2=A0 PUSH_MSR_REGS > >> +=C2=A0=C2=A0=C2=A0 WRMSR_ASM $MSR_IA32_SPEC_CTRL, $0, $0 > >=C2=A0 > I think you should be writing 2, not 0, since I'm reasonably > confident that we want STIBP on.=C2=A0 Can you explain why you're writing > 0? >=20 > Do we want to talk about STIBP in general?=C2=A0 Should it be (yet anothe= r) > boot option to enable or disable?=C2=A0 If there is STIBP support without > IBRS support, it could be a set and forget at boot time. We haven't got patches which enable STIBP in general. The kernel itself is safe either way with retpoline, or because IBRS implies STIBP too (that is, there's no difference between writing 1 and 3). So STIBP is purely about protecting userspace processes from one another, and VM guests from one another, when they run on HT siblings. There's an argument that there are so many other information leaks between HT siblings that we might not care. Especially as it's hard to *tell* when you're scheduling, whether you trust all the processes (or guests) on your HT siblings right now... let alone later when scheduling another process if you need to *now* set STIBP on a sibling which is no longer save from this process now running. I'm not sure we want to set STIBP *unconditionally* either because of the performance implications. For IBRS we had an answer and it was just ugly. For STIBP we don't actually have an answer for "how do we use this?". 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